In taking a scene against light or taking a scene large in luminance difference, a white-out or black-out effect may occur only with a standard image with the exposure period matched with the illuminance of photographic subject.
In order to overcome this problem, two or more non-standard images having different exposure times are taken to be replaced by an image obtained by multiplying the non-standard images by a synthesis gain in the area too bright or too dark in the standard image to enlarge the dynamic range of the resultant image, which is then compressed in match with the output bit.
In this case, the standard image and the non-standard image are connected by synthesized gain, so that an improper synthesized gain may cause false contouring in the boundary of connection.
So, as disclosed in Japanese Patent Laid-open No. Hei 7-131708, the difference in photoelectric conversion and so on due to the difference in incident light intensity can be ignored by obtaining a synthesis gain to be multiplied by the non-standard image by a ratio between two image signals in the pixel of long/short replaced luminance level.
However, if a smear occurred in a backlight scene for example, false contouring is caused by the computation of an improper synthesized gain (FIG. 1).
Also, when a moving subject is taken, signals at the same pixel positions in two or more images are not always by the same subject. In this case, an improper image signal ratio is obtained, so that an improper synthesized gain is computed, resulting in false contouring.